Preparation of smoking product of cellulose derivatives and process



United States Patent 3,491,766 PREPARATION OF SMOKING PRODUCT OF CEL- LULOSE DERIVATIVES AND PROCESS Theodore S. Briskin and Geoffrey R. Ward, Beverly Hills,

Calif, assignors to Sutton Research Corporation, Los Angeles, Calif., a corporation of Delaware No Drawing. Continuation-impart of applications Ser. No.

595,622, Nov. 21, 1966, and Ser. No. 674,994, Oct. 12,

1967. This application July 16, 1968, Ser. No. 745,135

Int. Cl. A24b 15/00 US. Cl. 1312 11 Claims ABSTRACT OF THE DISCLOSURE In the preparation of a smoking product, selective oxidation of cellulosic material with liquid nitrogen dioxide containing an amount of water up to 8% by weight and at an elevated temperature.

This is a continuation-in-part of our copending applications Ser. No. 595,622, filed Nov. 21, 1966, and entitled Smoking Products, and Ser. No. 674,994, filed Oct. 12, 1967, and entitled Smoking Products and Process for Making Such Products.

As used herein, the term smoking products is meant to refer to and to include filler material embodied in cigarettes, cigars and for use with pipes and the like, and mixtures thereof with various portions of tobacco and including cigarette papers and wrappers used in the prep aration of such cigars and cigarettes, and it includes cigarettes, and it includes cigarettes cigars and the like products manufactured with such filler materials and wrappers.

In the aforementioned copending applications, description is made of the preparation of a smoking product suitable for use in cigarettes, cigars or with pipes wherein the smoking product is prepared of relatively pure cellulosic materials subjected to selective oxidation with liquid nitrogen dioxide to convert preferably more than 90% of the methylol groups in the cellulosic molecule to yield a product which can be referred to as oxycellulose. The oxidation reaction product is further processed by removal of liquid nitrogen dioxide by vaporization and can be copiously washed with water and/or alcohol and/or acetone or other solvent for removal of solubilized foreign material, including oils, waxes, latices and the like, which contribute undesirably to the taste and aroma when used as a smoking product in accordance with the practice of this invention.

As further described in the aforementioned copending applications, the oxidized and cleansed cellulosic derivative is further processed by a reduction reaction with borohydrides of an alkali or alkaline earth metals such as sodium or lithium borohydride for reduction of nitrogen compounds, quinones, ketones and aldehydes which otherwise have a tendency to impart undesirable aroma and taste as the smoking product is burned. The product before or after reduction can be subjected to additional oxidation with a dilute peroxide solution as a means for eliminating further groupings which impart undesirable aroma or taste to the product.

The resulting smoking product is then formulated with mineralizing agents such as oxalates, glycolates, diglycolates, lactates, pivalates or tannates of such metals as calcium, magnesium, lithium, potassium, barium, strontium, or preferably introduced to form the salt internally in the cellulosic derivative for purposes of providing desired ashing characteristics. Instead of forming the described salts internally in the cellulosic derivative, limited beneficial characteristics can be achieved by external application of such mineralizing agents. As described, the desired internal 3,491,766 Patented Jan. 27, 1970 "ice introduction is achieved by first wetting the cellulosic de rivative with a dilute solution containing the metallic ion for absorption into the cellulosic derivative followed by exposure to a solution of the anion to precipitate the metal salt in situ in the cellulosic material.

- The treated cellulosic derivatives can be further processed to improve the burning, glow and smoking characteristics by formulation to include a potassium salt, such as potassium oxalate or by the addition of rubidium or cesium in the form of compounds thereof in amounts within the range of 0.1% to 10% by weight but preferably less than 1% by weight, as described in the copending application Ser. No. 623,528, filed Mar. 16, 1967, and entitled Smoking Products and Process for Their Manufacture. Smoke generators for improving the appearance of the smoke generated by the product can be introduced as by the introduction of various fatty acids and the like and the aroma and pH characteristics can be achieved by the addition of volatilizable alkalyzing material such as ammonia, nicotine and the like.

The resulting product is suitable for use as a smoking product alone or in admixture with tobacco to produce a smoking product having good taste, good aroma and good appearance.

This application will be addressed to the process for treatment of the cellulosic material with liquid nitrogen dioxide for selective oxidation of methylol groups in forming an oxidized cellulosic derivative which is more suitable for use as a smoking product than the purified cellulose and which finds excellent use in the preparation of a smoking product.

The features of this invention reside in the conversion of a cellulosic material to a product which is desirable for use in smoking and which finds wide acceptance as a smoking product from the standpoint of taste, aroma, appearance, burning characteristics and relative absence of harmful ingredients or undesirable reaction products.

As the cellulosic raw material, use can be made of various forms of cellulose, such as wood pulp, alpha-cellulose, flax, fibrous carbohydrates, seaweed carbohydrates, bamboo filaments, straw, cotton filaments, hemp, refined paper, filamentous gums and even plant leaves and the like fibrous materials in which the cellulosic components have been separated, all of which is hereinafter referred to as cellulosic material.

It is preferred to make use of a purified cellulosic material from which various of the sugars, proteins, colors, chlorophylls, lignins, oils, waxes, resins and latices have been removed since these lend considerably to the undesirable odor and taste from the smoking product.

Purified cellulose is unsatisfactory for use as a smoking product from the standpoint of taste, aroma and burning characteristics. This is believed to stem from the acids and aldehydes that are evolved upon pyrolysis of the cellulose. It has been found that many of the defects of pure cellulose can be greatly alleviated by conversion of the methylol groups to carboxyl groups to produce a product which readily pyrolyzes for complete breakup of the cellulosic molecule into water vapor, and oxidation products of carbon, such as carbon dioxide and low molecular weight compounds which readily volatilize. Thus the object is to achieve selective oxidation of the cellulosic material to convert methylol groups, especially the methylol groups on the C carbon, to carboxyl groups, with better than 30% and preferably with better than conversion. There is no objection to the ancillary oxidations, such as conversion of the secondary hydroxyl groups as on C and C to monoand di-keto groups so long as cleavage does not occur.

Selective oxidation without degradation of the cellulosic material is difiicult to achieve with oxidizing agents such as peroxides, hypochlorites, permanganates, dichromates and the like. On the other hand, selective oxidation for use in preparation of a smoking product from such cellulosic materials can be achieved with nitrogen dioxide.

Gaseous nitrogen dioxide has been found to be impractical for this purpose since the resulting oxidation reaction is too siow and difficulty is experienced in achieving complete access to the entire cross=section of the cellulosic derivative with gaseous nitrogen dioxide with the result that it is diflicult to achieve a commercial rate of conversion and conversion is not uniform thereby to produce an undesirable product for smoking. Further, the reaction of oxidation of the cellulosic material is an exothermic reaction that is accompanied by the generation of heat which is not easily dissipated with the use of gaseous nitrogen dioxide. As a result, hot spots can develop in various areas of the treated material to cause degradation and even combustion of the cellulosic materlal.

On the other hand, it has been found that liquid nitrogen dioxide yields an oxidation reaction that has the desired selectivity and that complete wet-out of the cellulosic materials can be achieved almost instantaneously with liquid nitrogen dioxide with the result that the oxidation reaction takes place substantially uniformly throughout the cross-section of the cellulosic material and at a much more rapid rate whereby a more uniformly and more completely oxidized product is obtained in lesser time. Furthermore, liquid nitrogen dioxide, when used in the proportions most suitable for the practice of this invention, operates as a quench immediately to dissipate heat generated by the exothermic reaction so as to avoid the formation of hot spots or non-uniformity in the reactions.

It has been found that the course of the oxidation reaction and the treatment of the oxidized cellulosic material can be influenced by a number of very important factors which cannot be translated into reactions with gaseous nitrogen dioxide but which can be employed in the oxidation of the cellulosic material with liquid nitrogen dioxide thereby greatly to enhance the oxidation process including increase in reaction rate, increase in the amount of conversion, uniformity of oxidation, as Well as purification and subsequent treatment of the oxidized reaction product, as will hereinafter appear.

In accordance with the practice of this invention, the oxidation of the cellulosic material is carried out by treatment of the cellulosic materiai in liquid nitrogen dioxide, often referred to as N in the ratio of 1 part by weight cellulosic material to 5 to 1000 parts by weight of liquid nitrogen dioxide and preferably 1 part by Weight cellulosic material to 25 to 50 parts by Weight of liquid nitrogen dioxide. Alternatively, the liquid nitrogen dioxide may be percolated through a mass of cellulosic a material and recycled so that the weight ratio of cellulosic material to nitrogen dioxide may be as great as 2 to l in the reaction zone. The reaction is carried out at a temperature within to 65 C. At atemperature below 15 C., the rate of reaction with liquid nitrogen dioxide is too slow for commercial practice and an excessive amount of hydrolytic cleavage is experienced, for a reason which will be explained shortly. At reaction temperatures in excess of 65 C., the oxidation reaction becomes less specific and undesirable side reactions take place to produce excessive amounts of by-products. In the preferred practice of the invention, use is made of a temperature above C. and preferably within the range of to C. at pressureswhich result from the vapor pressure of the liquid nitrogen dioxide plus the ambient pressure of any other atmosphere contained within the reaction vessel.

An important feature of this invention arises from the discovery that the oxidation reaction proceeds at a more rapid rate, other conditions being equal, when some water is added to the liquid nitrogen dioxide. Furthermore, while water is a beneficial component in combination with the liquid nitrogen dioxide in the oxidation of cellulosic materials, there are some very important factors which arise in the use of water as a component of the reactant, at least from the standpoint of the amount of water present and the temperature conditions employed when water is present as a part of the reaction medium.

Utilization of water as an ingredient in the reaction medium has previously been deemed undesirable because Water was believed to join with nitrogen dioxide to form strong acids that cause degradation and attack of the cellulosic materials. As a result, efforts have been made, by the addition of P 0 and desiccants, to effect removal of water as it is formed, inoxidations using gaseous nitrogen dioxide.

-It has been found that after five hours of reaction of cellulosic materials under positive pressure of about 30 to 50 pounds and at a temperature of 45 C. with the materials present in the ratio of 1 part by weight cellulosic material to 100 parts by weight of liquid nitrogen dioxide, the material becomes oxidized to 82% when water is absent from the oxidizing medium. However, the percent oxidation increases to 86% with 0.5% by weight water; 90% with 1% by weight water; 90% with 2% by weight water, and 83% with 4% by weight water. This indicates that the oxidation reaction rate increases with increased amounts of water in the reaction medium formed of liquid nitrogen dioxide with the optimum between about 1% to 3% water. With the larger water amounts, the yield dropped due to over reaction and degradation. Water in amounts greater than 8% could not be employed since the material was taken into solution in the liquid nitrogen dioxide. Thus a certain amount of water up to 8% by weight of the reaction medium is beneficial to the oxidation reaction insofar as the reaction rate is concerned.

A new and novel concept of this invention resides in the further discovery that the ionization effect, as measured by the electrical conductivity of the liquid nitrogen dioxide-water solution, is anomalously dependent upon temperature. It has been discovered that, as the temperature of the solution decreases, the e ectrical conductivity of the solution increases enormously instead of decreasing in a normal manner. As a result, it becomes possible by carrying out the reaction at higher temperatures to make use of a substantially non-ionizing reaction medium containing water Within the range described, without experiencing excessive degradation of side reactions by reason of the presence of ions of water or of acids. For example, a reaction mixture containing 2% by weight water in liquid nitrogen dioxide does not exhibit electrical conductivity at 20 C. whereas it is very highly conductive at 5 C. Similarly, a reaction mixture containing 4% to 5% by weight water in liquid nitrogen dioxide is relatively non-electrically conductive at 40 to 65 C. but is highly conductive at 15 to 20 C.

It will be apparent that the discovery of these phenomena enables the deveiopment of conditions most highly conducive to the most rapid rate of oxidation of the cellulosic material without bringing about excessive deterioration or degradation. By utilization of the described concepts, it becomes possible to make use of water and higher temperatures together to achieve a reaction rate with liquid nitrogen dioxide which was not heretofore believed possible. Under these conditions, it becomes possible to make use of higher concentrations of water with higher reaction temperatures and with higher reaction rates both to permit of batch processing in a commercially feasible amount of time per unit of equipment and to provide a basis for the development of a continuous process for the oxidation.

A further discovery consistent with the ionization phenomena revealed above is that during removal of the nitrogen dioxide at the end of the reaction, the cellulose becomes very conductive due to evaporative cooling of the nitrogen dioxide thereon and a build-up of mineral acids. At this point, appreciable degradation occurs. It is found that this can be avoided by rinsing with liquid nitrogen dioxide which is free of moisture. Since the reaction is substantially complete, no appreciable moisture is gen erated after this stage of the process in the relatively short interval before the drying.

These same concepts find no application or relationship to the use of a gaseous nitrogen dioxide system for oxidation of cellulosic materials. In such a system, a highly conductive acidic condition forms on the material, in the presence of water vapor, and it stays on the material when there is no liquid nitrogen dioxide to absorb it and de-ionize it. This leads to rapid degradation and attack of the cellulosic material whereby the gaseous process has little, if any, tolerance for water as a part of the reaction medium or on the cellulosic material and the gaseous nitrogen dioxide thus remains impractical for use.

Thus the concepts of this invention embody the selective oxidation of the cellulosic material with liquid nitrogen dioxide containing up to 8% by weight of water and preferably in an amount within the range of 1.5% to 3.0% by weight water at a temperature within the range of 15 to 65 C. and preferably at a temperature within the range of 15 to 25 C. when the amount of water is within the range of 0.5% to 2% by weight; 25 to 40 C. when the amount of water is within the range of 1.0% to 4.0% by weight, and 40 to 65 C. when the amount of Water is within the range of 1.5% to 5.0% by weight, with the reaction pressure corresponding to the vapor pressure of the N0 at the temperature conditions existing or to pressures higher than autogenous pressure.

Best yield 'is secured with water present in the liquid nitrogen dioxide in an amount within the range of about 2% il%. Since Water is continuously being formed during reaction, build-up of the concentration beyond the desired limits can be prevented by continuous recirculation of the reaction medium with the removal of only a fraction thereof and replacement with dry nitrogen dioxide liquid to make up for the amount removed. If, for example, when using liquid nitrogen dioxide containing 2% water, the water of reaction increases the amount of water present by /2% during the oxidation reaction, then the desired 2% level of water can be maintained by bleeding off one-fifth of the solution during the reaction with replacement by dry nitrogen dioxide liquid in the amount drained off. The deliberate use of such a water level for the reaction is an important advantage since it can be maintained by means of a nitrogen dioxide regeneration plant which is only one-fifth the size of that required to convert the nitrogen dioxide from /2% water back to 0% water.

A further concept of this invention resides in the discovery that formulation of the oxidizing medium by addition of water or aqueous material to the liquid nitrogen dioxide operates to adjust the specific gravity of the oxidizing medium more closely to approach the specific gravity of the cellulosic material. Under these circumstances, a more uniform and better suspension of the cellulosic material in the liquid oxidizing medium can be achieved and more easily maintained.

This type of reaction, with the cellulosic material suspended in the liquid reaction medium, provides for a more uniform wetting out of the cellulosic materials by the reaction medium and a more complete and uniform exposure of all of the cellulosic material to the oxidizing medium. As a result, the rate of reaction is increased and the reaction is made more uniform throughout the entire mass of cellulosic material thereby to produce a product which is more completely and more uniformly oxidized.

While the specific gravity of the cellulosic material may vary, from product to product, depending somewhat on the source and form of cellulosic material made available for the selective oxidiation reaction, and while the oxidizing medium may not be adjusted by aqueous addition exactly to conform with the specific gravity of the suspended solids, nevertheless, improved suspension characteristics with the described corresponding beneficial results are achieved by the formulation to include aqueous additions within the levels previously described for control of the reaction, such that the aqueous addition serves at least a dual purpose of increasing the rate of reaction and permitting increased reaction temperature as well as more uniform and better suspension of the cellulosic mate rials in the oxidizing liquid.

Having described the basic concepts of this invention, illustration will now be made by way of the following examples, which are given by way of illustration but not by way of limitation.

Example 1 A highly purified wood pulp is first fabricated into a thin paper web which is then shredded into strands of about 2 mm. width and loaded into a pressure vessel with liquid nitrogen dioxide containing 2% by weight water and in which the liquid reactant is introduced in the ratio of 1 part by weight pulp to 50 parts by weight of liquid oxidizing solution. The reaction vessel is heated by means of a heat exchange fluid circulated through an outer jacket to a temperature of 40 to 45 C. which results in a pressure of about 50 p.s.i.

For purposes of agitation, at small stream of the oxidizing liquid is continuously withdrawn from the bottom of the reaction vessel and returned to the top. During the reaction, liquid is removed from the system by bleeding from the liquid removed from the bottom of the reaction vessel for recirculation. The amount removed is replaced with dry liquid nitrogen dioxide whereby the water concentration in the liquid reactant is maintained at about 2% by weight.

After 24 hours, the oxidizing liquid is drained from the vessel and the oxidized cellulosic material is washed first with dry liquid nitrogen dioxide to remove acids and then it is freed of nitrogen dioxide by evaporation under reduced pressure, and in a current of dry air.

Upon removal, it will be found that the cellulosic material is oxidized by an amount better than 95% calculated on the basis of the maximum amount of polyanhydroglucuronic acid hypothetically possible.

Example 2 Purified cellulose wood pulp, previously treated for removal of lignin, sugars, proteins and water solubles, is loaded into a reactor with one hundred times its weight of liquid nitrogen dioxide containing 3 /2% by Weight of Water. The reaction vessel is heated for reaction at a temperature of about 50 C. for 5 hours with continuous recirculation of the oxidizing liquid from the bottom to the top of the reaction vessel. The reaction is carried out under autogenous pressure.

After completion of the reaction, the oxidizing liquid is drained from the vessel and the oxidized cellulosic material is washed first with dry liquid nitrogen dioxide and then with water until free from mineral acids.

The dried product will have better than of the methylol groups on C converted to the oxidized state with some of the secondary hydroxyl groups on C and C converted to ketone groups.

Example 3 Paper formed of purified alpha-cellulose is cut into strips and reacted in a reaction vessel with one hundred times its weight of liquid nitrogen dioxide containing 1.5 by weight of Water. The reaction is carried out in a jacketed reaction vessel in which the temperature can be controlled by circulation of a heat exchange fluid for a reaction temperature of 20 C. and at atmospheric pressure.

Agitation is maintained by recirculation of the liquid reactant through the vessel and the reaction is continued for four days. About one-third of the liquid reactant is replaced with dry nitrogen dioxide during the reaction to maintain the concentration of water at about 1.5%.

At the end of the reaction period, the solution is drained and the oxidized cellulosic material is Washed with several increments of Water to remove water solubles and to rinse off nitrogen dioxide. The dried product is 98% oxidized, when calculated as before.

The oxidized cellulosic material of Examples 1, 2 or 3 will be found to have improved smoking characteristics, from the standpoint of taste and aroma, as compared to the cellulosic material prior to the selective oxidation treatment. However, it is preferred further to process the oxidized cellulose derivative of Examples 1 to 3, as described in the aforementioned copending applications, to effect reduction reaction in the presence of ammonium, lithium, or sodium borohydride and possible oxidation before or after the reduction reaction with a very dilute solution of a peroxide followed by modification of the cellulose derivative to formulate the cellulose derivative with miner-alizing agents, such as calcium oxalate, for maintaining glow or the desired burning rate, such as compounds of cesium, rubidium or potassium, agents for producing smoke such as fats and esters, and possibly other agents such as ammonia for .pH control, carbon and the like materials for colorizing the product, and the like, all as described in the aforementioned copending applications.

It will be apparent from the foregoing that there is provided an improved process for selective oxidation of cellulosic materials to produce a product more suitable for use as a smoking material and in which the selective oxidation reaction can be carried out at a higher and more economical rate while achieving greater uniformity in oxidation of the cellulosic material thereby to produce a better product at a more reasonable rate.

It will be understood that changes may be made in the details of formulation and operation without departing from the spirit of the invention.

We claim:

1. In the preparation of a smoking product from cellulosic material comprising reacting the cellulosic material in an oxidizing medium formulated of liquid nitrogen dioxide containing up to 8% by weight water and at a temperature within the range of 15 to 65 C.

2. The process as claimed in claim 1 in which water is present in the reaction medium in an amount within the range of 0.5% to 5.0% by weight.

3. The process as claimed in claim 1 in which water is present in the reaction medium in an amount within the range of 1.5 to 3.0% by Weight.

4. The process as claimed in claim 1 in which the amount of water present in the reaction medium is with in the range of 0.5% to 2.0% by weight and the reaction temperature is maintained within the range of 15 to 25 C.

5. The process as claimed in claim 1 in which the amount of water present in the reaction medium is with in the range of 1.0% to 4.0% by weight and the reaction temperature is maintained within the range of 25 to 40 C.

6. The process as claimed in claim 1 in which the amount of water present in the reaction medium is within the range of 1.5% to 5.0% by weight and the reaction temperature is maintained within the range of 30 to C.

7. The process as claimed in claim 1 which includes the step of replacement of a fraction of the reaction -medium with anhydrous nitrogen dioxide for removal of water in an amount corresponding to the amount of water generated in the reaction.

8. The process as claimed in claim 1 which includes the step of washing the spent nitrogen dioxide from the product with fresh nitrogen dioxide prior to evaporating off the nitrogen oxides from the products.

9. Theprocess as claimed in claim 1 which includes the steps of separating the liquid reaction medium from .the oxidation reaction product when the oxidation reac' tion has been completed and then washing with aqueous medium to remove water solubles.

|10. The process as claimed in claim 9 which includes the steps of separating the liquid reaction medium from the oxidation reaction product and drying at reduced pressure to volatilize oif nitrogen oxides before washing with aqueous medium.

11. An oxidized cellulose derivative adapted for use in the preparation of a smoking product and prepared by the process of claim 1. I

7 References Cited I UNITED STATES PATENTS 3,007,917 11/1961 Pauling 260-212 3,364,200 1/1968 Ashton et a1. 260-212 FOREIGN PATENTS 702,918 2/1965 Canada.

MELVIN D. REIN, Primary Examiner U.S. Cl. X.R. 

